1. Field of the Invention
The present invention relates to a method for lapping two surfaces of a titanium disk or a titanium alloy disk used for a magnetic disk or the like by the use of abrasives.
2. Description of the Prior Arts
Since titanium and titanium alloy (hereinafter, simply referred to as "titanium") are good in cleanness and superior to aluminium and aluminium alloy (hereinafter, simply referred to as "aluminium") in heat resistance, they are very much expected to be used for a substrate of high-quality magnetic disk or the like. In the case of the magnetic disk, a high degree of flatness and smoothness of a surface thereof is required. Therefore, a technique of lapping titanium disk has been studied earnestly. There remain unsolved, however, problems in methods of lapping relative to the titanium disk which is very hard to process compared with aluminum alloy.
An aluminium substrate is generally lapped as follows: the aluminium disk to be lapped is put between two surface plates held in parallel with each other together with carrier in the state of being loosely inserted into an opening made in a disk-type carrier. A thickness of the carrier is smaller than that of the aluminium disk. Abrasives are fed into between the aluinium disk and said surface plate. Two surfaces of the aluminium disk are lapped by rotation and revolution of the carrier, a predetermined pressure being applied to the aluminium disk through the surface plates.
When this method of lapping, in which there are substantially not any problems in lapping of the aluminium disk, is applied to lapping of a titanium disk, since the titanium disk is not sufficiently held, the titanium disk can be damaged, having sprung out of the carrier, or when the titanium disk is reliably held, there can occur damages on the carrier due to resistance to lapping.